Some things to consider:
1-you need 2 lightpipe "cables" for this to work(002 out to Behringer IN, Behringer out to 002 in)
2-WC is not going to work as the 002 has no WC connections
3-make sure that Pro Tools is set so that Optical=ADAT(if its set for Optical=SPDIF, then it would not work as intended)
4-Clocking is critical to proper function. If you want the ADA8000 to be the master, go into PT Setup>Hardware and select Optical or ADAT as the clock source. If you want the ADA8000 to be the slave, leave the PT clock source as Internal and set the Behringer to sync to external(it should have an LED to indicate that it is locked to an external sync/clock.
Hope something here helps
